Apple repairs question

I have to bring in my work machine, 5K iMac. I am having some issues with the screen. Will have image retention in less then a minute. Not sure if that is the screen or the logic board/gpu. It is a real pain to bring it in because as I mentioned it is my work machine. Thankfully I still have my rMBP at home I can use while it is gone for service. The question I have is does Apple do repairs on site at Apple stores or do machines always get sent away for hardware issues?

Trying to get an idea of how long I will be working on a severely downgraded system.

via ehMac.ca http://ift.tt/2hAdpiH